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  • 1.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Characterisation of thermally modified wood for use as component in biobased building materials2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The building sector shows growing interest in biobased building materials. Wood components, here defined as ground or milled wood, i.e. by-products (residuals/residues) from wood processing, such as sawdust or shavings, are valuable raw materials for new types of durable biocomposites suitable for outdoor building applications. An important research question related to such composites is how to characterise and enhance molecular interactions, i.e. adhesion properties, between wood and binder components. Another challenge is the hygroscopicity of the wood component, which can lead to dimensional changes and interfacial cracks during exposure to varying moisture conditions. Thermal modification of wood reduces its hygroscopicity, thereby, increasing its durability, e.g. its dimensional stability and resistance to biodeterioration. The hypothesis is that the use of thermally modified wood (TMW) components in biocomposites can enhance their durability properties and, at the same time, increase the value of residues from TMW processing. The main objective of this thesis is to study and analyse the surface and sorption properties of TMW components using inverse gas chromatography (IGC), dynamic vapour sorption (DVS), X-ray photoelectron spectroscopy (XPS), and the multicycle Wilhelmy plate method. The aim is to gain a better understanding of the surface and sorption characteristics of TMW components to enable the design of optimal adhesion properties and material combinations (compatibility) for use in biocomposites, especially suitable for outdoor and moist building material applications. Samples of TMW and unmodified wood (UW) components of Norway spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) heartwood were prepared and analysed with respect to surface energetics, hygroscopicity, liquid sorption and resulting swelling. The work also included analysis of surface chemical composition, as well as influences of extractives and moisture sorption history. The effect of using TMW components in a wood plastic composite (WPC) exposed to a series of soaking-drying cycles in water was studied with a focus on water sorption, swelling and micromorphological changes. The IGC analyses indicate that TMW components of spruce have a more heterogeneous surface energy character, i.e. a distinctly higher dispersive part of surface energy for low surface coverages, than do UW components. This is suggested to be due to the higher percentage of hydrophobic extractives present in TMW samples. Lewis acid-base analysis indicates that both UW and TMW components from spruce have a predominantly basic character and an enhanced basicity for the latter ones. Results show that both the hygroscopicity and water liquid uptake are lower for TMW than for UW samples. Unexpectedly, a significantly lower rate of water uptake was found for the extracted UW of pine heartwood than for non-extracted samples. In the former case, this is presumably due to contamination effects from water-soluble extractives, which increase capillary flow into wood voids, as proven by a decrease in water surface tension. Water uptake as well as swelling was significantly reduced for the WPCs with TMW and hot-water extracted UW components compared with the WPCs with UW components. This reduction also resulted in fewer wood component-polymer interfacial cracks in the WPCs with the modified wood components.

  • 2.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Surface characterisation of thermally modified spruce wood and influence of water vapour sorption2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today there is growing interest within the construction sector to increase the proportion of biobased building materials made from renewable resources. By-products or residuals from wood processing could in this case be valuable resources for manufacturing new types of biocomposites. An important research question related to wood-based biocomposites is how to characterise molecular interactions between the different components in the composite. The hygroscopic character of wood and its water sorption properties are also crucial. Thermal modification (or heat treatment) of wood results in a number of enhanced properties such as reduced hygroscopicity and improved dimensional stability as well as increased resistance to microbiological decay.

    In this thesis, surface characteristics of thermally modified wood components (often called wood fibres or particles) and influencing effects from moisture sorption have been analysed using a number of material characterisation techniques. The aim is to increase the understanding in how to design efficient material combinations for the use of such wood components in biocomposites. The specific objective was to study surface energy characteristics of thermally modified spruce (Picea abies Karst.) under influences of water vapour sorption. An effort was also made to establish a link between surface energy and surface chemical composition. The surface energy of both thermally modified and unmodified wood components were studied at different surface coverages using inverse gas chromatography (IGC), providing information about the heterogeneity of the surface energy. The water vapour sorption behaviour of the wood components was studied using the dynamic vapour sorption (DVS) method, and their surface chemical composition was studied by means of X-ray photoelectron spectroscopy (XPS). Additionally, the morphology of the wood components was studied with scanning electron microscopy (SEM).

    The IGC analysis indicated a more heterogeneous surface energy character of the thermally modified wood compared with the unmodified wood. An increase of the dispersive surface energy due to exposure to an increased relative humidity (RH) from 0% to 75% RH at 30 ˚C was also indicated for the modified samples. The DVS analysis indicated an increase in equilibrium moisture content (EMC) in adsorption due to the exposure to 75% RH. Furthermore, the XPS results indicated a decrease of extractable and a relative increase of non-extractable compounds due to the exposure, valid for both the modified and the unmodified wood. The property changes due to the increased RH condition and also due to the thermal modification are suggested to be related to alterations in the amount of accessible hydroxyl groups in the wood surface. Recommendations for future work and implications of the results could be related to knowledge-based tailoring of new compatible and durable material combinations, for example when using thermally modified wood components in new types of biocomposites for outdoor applications.

  • 3.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Altgen, Michael
    Georg August Univ Gottingen, Wood Biol & Wood Prod, DE-37077 Gottingen, Germany.;Aalto Univ, Dept Bioprod & Biosyst, FI-00076 Aalto, Finland..
    Militz, Holger
    Georg August Univ Gottingen, Wood Biol & Wood Prod, DE-37077 Gottingen, Germany..
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Sorption and surface energy properties of thermally modified spruce wood components2018In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 3, p. 346-357Article in journal (Refereed)
    Abstract [en]

    The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratoryscale reactor at two different temperature (T) and relative humidity (RH) conditions, T = 150 degrees C and RH = 100% (TMW150), and T = 180 degrees C and RH = 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with that of the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher KB than KA number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher KB number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The KB was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

  • 4.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Laine, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Sedighi Moghaddam, Maziar
    SP Technical Research Institute of Sweden.
    Rohumaa, Anti
    Aalto University, Department of Forest Products Technology.
    Segerholm, Kristoffer
    SP Technical Research Institute of Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    The influence of log soaking temperature and thermal modification on the properties of birch veneers2016In: IRG Annual Meeting, IRG Documents , 2016Conference paper (Other academic)
    Abstract [en]

    In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.

  • 5.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Lillqvist, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Spoljaric, Steven
    Seppälä, Jukka
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Hughes, Mark
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wood-plastic composites made from thermally modified spruce wood components and effects of exposure to water-soaking-drying cyclesManuscript (preprint) (Other academic)
    Abstract [en]

    The over-all aim of this work is to gain more insight on the potential to use thermally modified wood (TMW) components in wood-thermoplastic composites (WPCs), ie a new type of biobased building material, here defined as TMWPCs, assumed to have significantly increased moisture resistance and durability related to conventional WPCs. The specific objective was to prepare lab-scale TMWPCs and WPC controls with unmodified wood (UW), and to expose these samples to a series of severe water-soaking-drying cycles to study the effects on the water sorption behavior and resulting dimensional and micromorphology changes. TMW was prepared by thermal modification of a spruce board in an atmosphere of superheated steam at atmospheric pressure with a peak temperature of 210°C (also matched with an UW board as control). TMW and UW components were then prepared by a Wiley mill and thereafter sifted into a smaller (0.20-0.40 mm) and a larger (0.40-0.63 mm) size fraction. A portion of the wood components were also hot-water extracted (HE) with liquid hot-water. Composite samples with these different wood components, polypropylene (PP) matrix, and maleated PP (MAPP) as coupling agent (50/48/2 wood/PP/MAPP ratio) were then prepared by using a Brabender mixer followed by hot-pressing. The matching micromorphology of the composites before and after the soaking-drying cycles was analyzed using a surface preparation technique based on UV-laser ablation combined with scanning electron microscopy (SEM). An effort was also made to study the wood-thermoplastic interfacial behavior in the composites by dynamic mechanical analysis (DMA). The results of the water absorption tests showed, as hypothesized, a significantly reduced water absorption and resulting thickness swelling for the TMWPCs compared with the controls. Similarly, the WPCs with HE-UW components showed a significant reduction in water absorption and thickness swelling compared with the controls. In contrast, the samples with HE-TMW components resulted in only minor moisture property changes. These observations were also in agreement with the micromorphology analysis of the composites before and after the moisture cycling which showed a more pronounced wood-plastic interfacial cracking (de-bonding) as well as other microstructure changes in the controls compared with those prepared with TMW and HE-UW components. The DMA indicated better dispersion and increased interfacial interaction for the WPCs with UW components with the smaller size fraction compared with the larger size fraction. The loss modulus and storage modulus were overall reduced for samples with HE and TMW components compared with those with UW components. Based on these observations it is suggested that a potential biobased building material with increased durability for applications in harsh outdoor environments may be tailored as a TMWPC with a well-defined and comparably small size fractions of TMW components.

  • 6.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Moghaddam, Maziar Sedighi
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Liquid sorption, swelling and surface energy properties of unmodified and thermally modified Scots pine heartwood after extraction2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 3, p. 251-258Article in journal (Refereed)
    Abstract [en]

    The effect of extractives removal on liquid sorption, swelling and surface energy properties of unmodified wood (UW) and thermally modified Scots pine heartwood (hW) (TMW) was studied. The extraction was performed by a Soxtec procedure with a series of solvents and the results were observed by the multicycle Wilhelmy plate method, inverse gas chromatography (IGC) and Fourier transform infrared (FTIR) spectroscopy. A significantly lower rate of water uptake was found for the extracted UW, compared with the unextracted one. This is due to a contamination effect in the latter case from water-soluble extractives increasing the capillary flow into the wood voids, proven by the decreased water surface tension. The swelling in water increased after extraction 1.7 and 3 times in the cases of UW and TMW, respectively. The dispersive part of the surface energy was lower for the extracted TMW compared to the other sample groups, indicating an almost complete removal of the extractives. The FTIR spectra of the extracts showed the presence of phenolic compounds but also resin acids and aliphatic compounds.

  • 7.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Ormondroyd, Graham
    Biocomposites Centre, Bangor University, United Kingdom.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden, Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden, Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Surface energy characteristics of refined fibres at different pressures2014In: Proceedings of 10th Meeting of the Northern European Network for Wood Science & Engineering (WSE 2014) / [ed] Wilson, Peter, 2014, p. 134-138Conference paper (Other academic)
    Abstract [en]

    Wood fibres were produced on the pilot scale refiner at the BioComposites Centre, Bangor University, from a commercially sourced mix of chipped wood. The fibres were produced at refiner pressure 4, 6, 8 and 10 bar and dried in the associated flash drier. Surface energy characterization of the refined fibres was performed using inverse gas chromatography (IGC). The dispersive part of the total surface energy was analysed for duplicates of fibre samples at the four different refiner pressures. Non-polar alkane probes were used for the dispersive surface energy analysis at different surface coverage. Results indicate that the processing pressure has an effect of the dispersive surface energy and IGC analysis could be developed as a tool both for process development and process control in refining fibres.

  • 8.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Aalto University, Department of Forest Products Technology.
    Johansson, Leena-Sisko
    Aalto University, Department of Forest Products Technology.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    SP Technical Research Institute of Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Laine, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Aalto University, Department of Forest Products Technology.
    Surface chemical analysis and water vapour sorpion of thermally modified wood exposed to increased relative humidity2015In: The Eighth European Conference on Wood Modification (ECWM8) 2015 / [ed] Mark Hughes, Lauri Rautkari, Tuuli Uimonen, Holger Militz and Brigitte Junge, 2015Conference paper (Other academic)
    Abstract [en]

    The increased interest in environmentally friendly building materials is accompanied with an increased need for research on thermally modified wood. Products made from recycling or reusing of thermally modified residuals will have advantages in terms of environmental aspects. Surface characteristics of thermally modified wood play an important role for the development of applications involving bonding processes, for example when using thermally modified wood residuals in biocomposites. Surface chemistry characteristics are important in developing such materials. A technique used for surface chemical analysis of the outermost surface is X‑ray photoelectron spectroscopy (XPS). Some surface chemical analyses of wood and modified wood can be found in Nzokou and Kamdem (2005), Inari et al. (2006), Bryne et al. (2010), Johansson et al. (2012), Rautkari et al. (2012). Furthermore, the influence of water and moisture has crucial effect on the properties of wood and wood products. Water vapour sorption properties of hygroscopic materials can be studied using a dynamic vapour sorption (DVS) instrument. Previous studies on thermally modified wood exposed to several sorption cycles using DVS have shown an increase in hysteresis during the first cycle, compared with unmodified wood (Hill et al., 2012). However, during the second and the third sorption cycle a reduction in sorption hysteresis was observed.

     

    The objective of this work was to study the surface chemical composition and water vapour sorption properties of thermally modified wood. In particular, an effort was made to study any influence on such properties due to a previous exposure to a high relative humidity (RH). Interpretations of the results indicate a decrease of extractable or volatile organic components and a relative increase of non-extractable components, for the high humidity-exposed samples. This could be due to remaining extractives migrating towards or redistribution at the wood surface layer as a result of moisture diffusion. The DVS results show that the thermally modified wood samples that had been exposed to the high relative humidity condition revealed a slight decrease of the hysteresis of the sorption isotherms. The opposite trend was furthermore seen for the unmodified wood.

  • 9.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Department of Forest Products Technology, Aalto University.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Johansson, Leena-Sisko
    Aalto University, Finland.
    Campbell, JM
    Department of Forest Products Technology, Aalto University.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden, Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Laine, Kristiina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst)2016In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 7, no 3, p. 116-123Article in journal (Refereed)
    Abstract [en]

    The objective of this work was to study the hygroscopicity and surface chemical composition of thermally modified (TM) spruce. An effort was also made to study if those features were influenced by a previous exposure to a significant increase in relative humidity (RH). TM and unmodified Norway spruce (Picea abies Karst) samples, both in solid and ground form, were prepared. Water vapour sorption characteristics of the ground samples were obtained by measuring sorption isotherms using a dynamic vapour sorption (DVS). The surface chemical composition of the solid samples, both acetone extracted and non-extracted, were analysed using X-ray photoelectron spectroscopy (XPS). The DVS analysis indicated that the TM wood exposed to the 75% RH revealed a decrease in isotherm hysteresis. The XPS analysis indicated a decrease of acetone extractable or volatile organic components and a relative increase of non-extractable components for the samples exposed to the increased RH condition.

  • 10.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Department of Forest Products Technology, Aalto University.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Johansson, Leena-Sisko
    Department of Forest Products Technology, Aalto University.
    Campbell, Joseph
    Department of Forest Products Technology, Aalto University.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Water vapour sorption characteristics and surface chemical composition of thermally modified spruceManuscript (preprint) (Other academic)
  • 11.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Wood Material Science and Technology, Department of Forest Products Technology, Aalto University.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden.
    Water vapour sorption properties and surface chemical analysis of thermally modified wood particles2014In: Recent Advances in the field of TH and THM Wood Treatment, 2014Conference paper (Other academic)
  • 12.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, Dennis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Surface energy characterization at different moisture levels of thermally modified wood using inverse gas chromatography2013In: Proceedings of the 9th meeting of the Northern European Network for Wood Science and Engineering (WSE) / [ed] Briscke, C. & Meyer, L., 2013, p. 130-135Conference paper (Other academic)
  • 13.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Surface energy characterization of thermally modified wood particles exposed to humidity cycling using inverse gas chromatography2014In: / [ed] Nunes, L., Jones, D., Hill, C. and Militz, H., 2014Conference paper (Other academic)
    Abstract [en]

    The objective of this work was to study surface energetics of thermally modified wood particles exposed to dry-humid cycling. This information can give insight in the adhesion properties between the modified wood and composite matrices, adhesives or coatings. The surface energy characterization as well as the dry-humid cycling was performed using inverse gas chromatography (IGC). Duplicates of thermally modified and unmodified spruce particles with size 0-0.125 mm were investigated and conditioned in dry-humid cycles at 0-75 % RH and 0‑25 % RH. The BET specific surface area as well as the dispersive surface energy heterogeneity (or distribution) at different surface coverage was determined. The results showed similar trends for the different cycles in the dry and humid states, respectively. The difference in dispersive surface energy distribution between the dry and humid state was more pronounced at the lower surface coverage.

  • 14.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, Dennis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Surface energy characterization of thermally modified wood using inverse gas chromatography2013Conference paper (Other academic)
    Abstract [en]

    The objective of this work is to characterize surface energetics of thermally modified wood. Such information may be useful for a better understanding and predictions of adhesion properties between the modified wood and other material systems, e.g. coatings, adhesives or matrices in composites. Inverse gas chromatography (IGC) was used to study the surface energy characteristics of thermally modified spruce in particle form. Two different wood component samples were prepared, one with a larger and one with a smaller particle size distribution. Measurements of BET specific surface area and dispersive surface energy distribution of the particle samples are presented. Results indicate that a ground wood component of a finer size distribution of thermally modified wood is less energetically heterogeneous compared with a component with a larger size distribution.

  • 15.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, Dennis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Physico-chemical characterization of THM modified wood using inverse gas chromatography (IGC)2013In: Evaluation, processing and prediction of THM treated wood behaviour by experimental and numerical methods, 2013, p. 35-36Conference paper (Other academic)
  • 16.
    Källbom, Susanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden.
    Jones, Dennis
    SP Technical Research Institute of Sweden.
    Surface energy characterization of thermally modified spruce using inverse gas chromatography under cyclic humidity conditions2015In: Wood and Fiber Science, ISSN 0735-6161, Vol. 47, no 4, p. 410-420Article in journal (Refereed)
    Abstract [en]

    The surface energy of unmodified and thermally modified spruce wood components was researched at dry and moist conditions using inverse gas chromatography. The results indicate a more pronounced heterogeneous nature of the thermally modified wood surfaces in terms of the dispersive (nonpolar) component of the surface energy, compared with that of the unmodified wood surfaces. The dispersive component of the surface energy of the thermally modified wood ranged between 44 and 38 mJ/m(2) corresponding to an increase in surface coverage from a low level and up to about 10%. Suggested explanations for the more distinct heterogeneity of the thermally modified wood sample are related to chemical changes of the wood substance which seem to result in certain micromorphological features observed by scanning electron microscopy as alternated fracture surfaces created in the grinding process; and also possible changes or redistribution of the wood extractives. An increase of the MC, representing a change from a dry condition of approximately 0% RH to ca 75% RH, of both the unmodified and thermally modified samples seemed to have a marginal influence on the dispersive component of the surface energy. Possible implications of the results in this study can be found in the tailoring of new compatible and durable material combinations, for example, when using thermally modified wood residuals as a component in new types of biocomposites.

  • 17.
    Laine, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Tech Res Inst Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Department of Forest Products Technology, Aalto University.
    Hughes, Mark
    Department of Forest Products Technology, Aalto University.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, Dennis
    SP Tech Res Inst Sweden.
    Hardness, set-recovery and micromorphology studies of densified and thermally modified wood2015Conference paper (Other academic)
    Abstract [en]

    The purpose of the work reported in this paper was to increase the density of Scots pine wood in order to improve its hardness. Density was increased by compressing the porous structure of wood between heated metal plates in the radial direction by 40, 50 or 60% of the thickness. The compressed state was stabilised by thermally modifying (TM) the samples at 200 °C under steam conditions for 2, 4 or 6h. Set-recovery was almost eliminated (<1%) with TM of 6h for samples compressed 40 and 50%. It was discovered that hardness of densified wood was in some cases even three times higher compared to untreated wood. However, the hardness of the densified, non-TM wood was reduced after soaking and drying back to the original untreated level, while TM of 4 and 6h maintained an increased level of hardness.

  • 18.
    Lillqvist, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Lahti Univ Appl Sci, Fac Technol, Mukkulankatu 19, Lahti 15101, Finland.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Altgen, Michael
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Belt, Tiina
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Rautkari, Lauri
    Aalto Univ, Dept Bioprod & Biosyst, POB 16300, Aalto 00076, Finland.
    Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder2019In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 12, p. 1059-1068Article in journal (Refereed)
    Abstract [en]

    The objective of the study was to investigate the water vapour sorption behaviour of thermally modified (TM) wood powder, e.g. ground wood prepared from waste streams of TM solid wood, and wood powder that was extracted in pressurised hot water. Solid spruce wood was TM in steam conditions (210°C for 3 h), milled and hot-water-extracted (HWE) at elevated pressure (140°C for 1 h). The results evidence that the hot-water extraction reduced the water sorption and the accessible hydroxyl group concentration by the removal of amorphous carbohydrates. In contrast, the enhanced cross-linking of the cell wall matrix and the annealing of amorphous matrix polymers during thermal modification reduced the sorption behaviour of wood additionally, without further reducing the hydroxyl accessibility. These additional effects of thermal modification were at least partially cancelled by hot-water extraction. The results bring novel insights into the mechanisms that reduce the water vapour sorption of wood by compositional and structural changes induced by heating.

  • 19.
    Lillqvist, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rohumaa, A
    LaBoMaP, Ecole Nationale Supérieure d'Arts et Métiers.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Aalto University.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    THE INFLUENCE OF THERMAL MODIFICATION ON VENEER BOND STRENGTH2017In: Proceedings of the 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29 / [ed] Engelund Thybring, E., 2017, p. 56-Conference paper (Other academic)
    Abstract [en]

    The purpose of this study was to investigate the effect of thermal modification on birchveneer properties relevant in plywood manufacture. The wood material used in thisstudy was a birch (Betula pendula Roth) stem sectioned into small logs nominally 1.2 min length. The logs were completely immersed in a water tank heated to either 70 °C or20 °C. The soaked logs were rotary cut on an industrial scale lathe (Model 3HV66;Raute Oyj, Lahti, Finland) into veneer with a nominal thickness of 0.8 mm.Veneer specimens (150x150 mm2) were cut and thermally modified at 200°C in steamconditions for 2, 4 and 8 h. Mass loss and equilibrium moisture content (EMC) weremeasured after modification. The bond strength of the veneers was measured withautomated bonding evaluation system (ABES- Adhesive Evaluation Systems, Inc.,Corvallis, Oregon, USA) using phenol formaldehyde (PF) resin (Prefere 14J021, PrefereResins Finland Oy, Hamina, Finland). Specimens (20 x 117 mm2), were cut from theconditioned veneer sheets. A liquid PF resin was applied to an area of 5 x 20 mm2 atone end of the veneer specimens (approx. spread rate 100 g m-2). After adhesiveapplication, the veneer-resin assembly was placed into the ABES and after 180 s ofpressing (130 °C and 2.0 MPa) the shear strength of adhesive bond was measured.As expected from previous studies, the mass loss increased and EMC reduced withlonger thermal modification time. No significant difference in mass loss or EMCbetween log soaking temperatures was recorded in this study. The thermal modificationslightly reduced the bond strength; however, longer treatment time did not furtherreduce the bond strength. Therefore, based on this study, thermally modified veneerscould be successfully bonded and

  • 20.
    Lillqvist, Kristiina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rohumaa, Anti
    LaBoMab - Ecole Nationale Supérieure d'Arts et Métiers.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Rautkari, Lauri
    Department of Bioproducts and Biosystems, Aalto University.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    The influence of thermal modification on veneer bond strength2017Conference paper (Other academic)
  • 21. Ormondroyd, G. A.
    et al.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Curling, S. F.
    Stefanowski, B. K.
    Segerholm, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jones, D.
    Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, p. 1-8Article in journal (Refereed)
    Abstract [en]

    During fibre processing, wood fibres are subjected to a range of physical and chemical conditions sufficient to slightly alter their chemical composition and hence their ultimate performance when used in the manufacture of wood fibre-based composites. In order to better understand the effects of refiner conditions on material performance, wood fibres were subjected to processing at different refiner pressures (4, 6, 8 and 10 bar) and subsequently dried in a flash drier. The fibres were analysed for changes in surface area, surface energy, surface structure and water vapour sorption characteristics. The methods applied were nitrogen adsorption utilising the Brunauer–Emmett–Teller theory, inverse gas chromatography, scanning electron microscopy and dynamic vapour sorption. It was found that increasing refiner pressure resulted in fibres of lower surface area, accompanied by increasing dispersive surface energies up to operating refiner pressures of 8 bar. It was found with fibres refined at different pressures that as the refiner pressure increased the equilibrium moisture content of the fibre decreased at the set relative humidities. However, it was also noted that the hysteresis was not significantly different between each of the refiner pressures. The results suggest that different refiner pressures can be used to tune the surface characteristics which may be beneficial to product development and the improvement of the environmental profile of the wood fibre composites.

1 - 21 of 21
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